(PVC/TPO)-The most common thermoplastic roof membranes are PVC and TPO. The following provides general descriptions of these two systems.
Polyvinyl Chloride (PVC)
PVC sheets are produced by calendaring, spread coating or extruding, and typically are reinforced with polyester or glass-fiber mats or scrim. PVC sheets contain plasticizers and stabilizers, as well as other additives to impart flexibility and achieve other desired physical properties. Some membranes are available with nonwoven fleece backing adhered to the underside of a sheet.
- Sheet widths range from 6 feet to 12 feet wide.
- Sheets are typically 45 mils to 90 mils thick.
- Seams are sealed by heat or chemical welding.
- PVC membranes are produced in numerous colors, though gray and white are the most common.
PROS
- Strength
PVC roofs are very strong. The American Society of Testing and Materials (ASTM) requires a minimum breaking strength of 200 pounds per inch. All the ones I’ve worked with have a minimum breaking strength of 350 lbs/in. That probably doesn’t mean much to you, the reader, but trust me, it’s strong.
- Chemical resistance
Chemicals on a roof are not uncommon on top of manufacturing facilities and restaurants. PVC roofs are very resistant to chemical damage. Animal fat from grease vents on restaurants can damage an asphalt-based roof and some other single-ply roofs, but it won’t hurt a PVC roof.
- Fire resistance
PVC roofs have a good fire-resistance rating. This can be intensified by using different types of roof insulation under the PVC.
- Wind resistance
Because of their strength and different types of installation procedures, PVC roofs have great wind uplift resistance. This is important if you live a high wind area like along coasts, in Amarillo or Chicago or the High Plains of Eastern New Mexico, or have a high-rise building.
- Ease of installation
Compared to asphalt-based roofing, PVC roofs are easy to install. There is no kettle, there are no torches, all the corner pieces, pipe flashings, and several other flashing components are pre-made, thereby easily installed. There are a lot less seams with PVC roofs that with asphalt-based roofs, too. However, the seams take more time to deal with.
CONS
- Thickness
PVC roofs are roughly as thick as other single-ply roofs, but not nearly as thick as asphalt-based roof systems. This makes them more susceptible to damage. If you have heavy foot traffic on your roof, then you may want to consider an asphalt-based roof.
- Slick
All roofs can be slick, but PVC roofs can be very slick. You have to be carefully when you walk, especially if the roof is wet.
- Plasticizer leaching
The plasticizers in PVC roofs will leach out over time, meaning they won’t last forever. However, the plasticizer technology has greatly improved and you can get a high quality roof if you buy a PVC roof.
- Shrinking over time
This probably has to do with the previous item, but PVC roofs can stretch or shrink over time (mostly shrink). This causes roof failure. It’s not something that usually happens right away, it takes years and years. You just need to keep an eye on the roof. Usually, the bigger the roof, the greater the severity of the problem because they’re only going to shrink a certain amount.
PVC and TPO roof membranes can be installed fully adhered, mechanically attached or ballasted. Most PVC and TPO membranes do not receive surfacing. Our manufactures, Elevate, and Versico offer total system warranties ranging from 5 to 30 years depending on system type, material thickness and Factory Mutual (FM), and Underwriters Laboratories (UL) ratings.
